Light is one of nature's ways of moving energy from one place to another. It has no substance, or mass. How does light travel? Light behaves like a traveling wave, something like waves in a string or on the surface of water. The waves are very small, so we don't see them, but go out into the sunlight, and you can feel the energy in the form of heat. Light can also behave like a stream of particles, but we're just going to look at some basic things that make it look like a wave.

All light waves travel ata speed of about 300,000 (300 thousand) kilometers per second in a vacuum such as space. That's about 186,000 miles every second. That means light can travel almost eight times around the Earth in a second. That's pretty fast! Light has slightly slower speeds when it travels through denser material such as a planet's atmosphere or a piece of glass, but we don't notice the difference.

There are many different kinds of light besides the light you can see. What do you think is a good word to describe the light you see? Scientists often describe the light you can see as "visible" light. The entire range of different kinds of light including the ones the human eye cannot see is called the electromagnetic spectrum. Can you think of some other types of light besides visible light? You'll be trying to figure out the different types of light that make up the electromagnetic spectrum as you go through this light tour!